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I am trying to get a handle on this static route thing, but just can't seem to do it. I don't know if I'm over thinking it or what. Please see the attached pictures from my packet tracer exercise. I am grateful to any and all assistance

I need to get from the ISP router to Branch1 and PC1. Branch2 and PC2 by adding the correct static routes to Branch1 router and Branch2 router.

I guess what I would like to know is this: based on the above addressing scheme, what would I use for the route to get from branch1 to branch2, and from branch2 to isp and from branhc2 back to branch1?

What confuses me is the interfaces I need to be using. Do I use only the ethernet as the destination address, or do I use the serial connection first, and THEN the ethernet?

I hope I am being a little more clear on what I need.

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Steve
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2 Answers2

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There appears to be a couple bugs in your pictures. PC2 has a gateway that is the same as its IP, PC2 probably should have a gateway of 172.16.15.1. PC0, and ISP Fa0/0 are connected but have a different mask (one is 16, and the other 24), I will assume a 24 bit mask below.

When working out routing, I find it is easiest to draw a picture that looks like the image below. Basically you draw a picture with all the IP and subnet written next to each device.

e below that start adding route table information. The basic rule is that a router will need a static route for every network that it is not directly attached to, and cannot be handled by a default route. So Branch1 is not attached to 172.16.15.0/24 (Branch2/PC2), so you will need a route on Branch1 for Branch1 or PC1 to reach that network.

Another step that helps is to build yourself a table of the IP networks. So in the above network these are mentioned.

10.10.0.0/24
172.16.4.0/24
172.16.15.0/24
192.168.1.4/30
192.168.3.8/30
192.168.1.4/30

Once you have your table, look at a single router, and figure out what the next hop will be for each network. So Branch1 is connected to 3 of these networks. This means that the Branch1 router will most likely need 3 routes for it to forward traffic to the correct locations (assuming no default).

So the route table of Branch1 would look like this

10.10.0.0/24     via 192.168.1.5
172.16.4.0/24    no route - Directly connected
172.16.15.0/24   via 192.168.2.2
192.168.1.4/30   no route - Directly connected
192.168.3.8/30   via 192.168.2.2
192.168.2.0/30   no route - Directly connected

Because of your topology you could also add a couple more routes with a different metric to handle the case of one of the links going down between the routers.

10.10.0.0/24     via 192.168.2.2
172.16.15.0/24   via 192.168.1.5
192.168.3.8/30   via 192.168.1.5

router diagram

Zoredache
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  • So, according to you diagram, I would have to add the route like this (from branch1) ip route 192.168.1.0 255.255.255.252 172.16.15.0. Or, am I not doing this right? – Steve Feb 18 '11 at 19:34
  • @Steve, that is not a valid route, because your network doesn't have a 192.168.1.0/30 subnet anywhere and 172.16.15.0 is not a valid IP or used on any of your routers. – Zoredache Feb 18 '11 at 21:08
  • BTW: Those are Ciscos addressing schemes. :) – Steve Feb 18 '11 at 22:48
  • I would like to apologize for my first attempt at a question. Since I was unclear myself what I needed to ask, it was difficult for me to put into words what I wanted to convey. Thank you for understanding. – Steve Feb 18 '11 at 23:00
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Your question is unclear! First, you have to understand routing in general to be able to understand static routing.

Static routing is done by telling your router manually (using commands) where it can find the path for a specific network. Have a look at this link. This distinguish it from dynamic routing in which the router discovers the required path by exchanging routing information with other neighboring routers.

Khaled
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